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Abstract:Urban flooding is an increasing problem in developing countries, thus understanding flood dynamics is necessary to establish guidelines on urban development and flood management. This paper studied the lower reaches of the Andalien River basin, situated on the coast of the Greater Concepcion Metropolitan Area (CMA), the second most urbanized area in Chile. This basin experienced a record 21 flood events in the last 50 years. Patterns in the evolution of urban growth were evaluated using a historical analysis ) that specifically focused on how these patterns interact with zones that are prone to flooding over different return periods. Our model applied to the CMA, but is sufficiently transversal to be applied in similar areas. It was determined that the built-up area increased by 1457 ha and had an urban form vulnerable to future flooding due to its location on landforms exposed to flood risk, with altitudes of <8 m and slopes of <0.5 • . The bankfull channel of the Andalien River lost 18.4% of its area. Upstream, management of the river decreased smaller floods for a return period of two, five, and 10 years; however, for a return period of 500 years, risk remained at high levels. These findings help to rethink and improve urban planning and the response of Chilean cities in relation to flood hazard.

Natural disasters can cause abrupt disturbances in coastal wetlands, affecting the social perception of ecosystem services (ES). The Tubul-Raqui coastal wetland is one of the most important wetlands in south-central Chile. Rich in biodiversity, these wetlands provide ES to a population of 2238 inhabitants. The recent M W = 8.8 earthquake of 2010 caused a coastal uplift of 1.4 m and substantial morphological, social, and environmental changes. This paper analyzes the social perceptions of the inhabitants of the village of Tubul-Raqui following a large earthquake disturbance with regards to ES provision frequency and their future changes. A statistically representative semi-structured survey was conducted (175 valid surveys) and the data interpreted through factor analysis and statistical tests for independent categorical variables. The perception of cultural and regulating services was significantly greater than that of provisioning services, which were probably the most affected by the earthquake. Residents identified habitat for species, recreation, and hazard regulation as the most important ES. Perception was influenced by the categorical variables of gender, age, and ethnicity; for example, hazard regulation services varied strongly by gender. According to the respondents, the availability of ES will remain stable (50%) or decrease (40%) in the next 50 years, mainly due to anthropogenic drivers; the effect of natural disasters was not mentioned among the main drivers of change.

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